docs: def schnorr_partial_combine(self, schnorr_sigs):
          """Combine multiple Schnorr partial signatures."""
          if not HAS_SCHNORR:
              raise Exception("secp256k1_schnorr not enabled")
          assert len(schnorr_sigs) > 0
  
          sig64 = ffi.new('char [64]')
          sig64sin = []
          for sig in schnorr_sigs:
              if not isinstance(sig, bytes):
                  raise TypeError('expected bytes, got {}'.format(type(sig)))
              if len(sig) != 64:
                  raise Exception('invalid signature length')
              sig64sin.append(ffi.new('char []', sig))
  
          res = lib.secp256k1_schnorr_partial_combine(
              self.ctx, sig64, sig64sin, len(sig64sin))
          if res <= 0:
              raise Exception('failed to combine signatures ({})'.format(res))
  
          return bytes(ffi.buffer(sig64, 64))